Pot Height vs. Effenciency

[robbybob1]

Hello again!

I just tried another interesting stove test using my Pepsi Can Alcohol stove that you guys might be interested in. I tried 2 different things:

1) I shrunk down my standard stove from 1 1/2" to 13/16" (It looks like a Flying Saucer now!). I did this to examine the theory that a smaller volume of the stove would make it use less fuel to boil water (some people call this "Efficiency"). By cutting the volume in half, the performance DID NOT get any better than my standard stove. In fact, the boil times were remarkably similar.

2) I took the same 2 stoves and decreased the distance from the stove to the pot from 1 3/8" to 1/2". I put 1/2 oz (15ml) of Denatured alcohol in, with 16 oz of 45 deg. water in a Walmart Grease pot painted with High Temperature Grill Paint and an Oven Liner windscreen. At the 1 3/8" pot height, the max temp of the water was 175 deg. and the burn time for both stoves was about 3 1/2 minutes. When I put them at 1/2", both stoves boiled the water at 8 min and 20 sec, and burned for a total of 10 minutes. Remember, the only thing that changed was the pot height.

Anyway, I would appreciate anyone out there who would like to try this test using their favorite setup and then putting a spacer under the stove to set the pot height at 1/2", and report back the information here. Thanks again!

robbybob1

[Streamweaver]

I did the oposite,I had a short soda stove that used about 3/4 oz of fuel to boil my water for tea on dayhikes and I wanted a stove a bit bigger to boil more water and for cooking food. the bigger stove which was built exactly the same but about a half inch taller filled with the same amount of fuel failed to boil the same amount of water.I tried it twice so far with the same results using the same setup as the other stove and Im not sure why this is happening. It could simply be the fact that it is quite a bit colder than it was when i was using the smaller one. maybe Ill try a test indoors using both and see what happens. Erik

[SGT Rock]

Originally posted by robbybob1
Hello again!

I just tried another interesting stove test using my Pepsi Can Alcohol stove that you guys might be interested in. I tried 2 different things:

1) I shrunk down my standard stove from 1 1/2" to 13/16" (It looks like a Flying Saucer now!). I did this to examine the theory that a smaller volume of the stove would make it use less fuel to boil water (some people call this "Efficiency"). By cutting the volume in half, the performance DID NOT get any better than my standard stove. In fact, the boil times were remarkably similar.


I think you will only find a difference if you are using a pressurized design. Otherewise the only benifit to shrinking a stove would be better stability and lighter weight.


2) I took the same 2 stoves and decreased the distance from the stove to the pot from 1 3/8" to 1/2". I put 1/2 oz (15ml) of Denatured alcohol in, with 16 oz of 45 deg. water in a Walmart Grease pot painted with High Temperature Grill Paint and an Oven Liner windscreen. At the 1 3/8" pot height, the max temp of the water was 175 deg. and the burn time for both stoves was about 3 1/2 minutes.


Sounds about right. Too much distance from the flame to the pot is wasting fuel. I say waste, because it allows a lot of air to get in and allow the fuel to combust as rapidly as possible. I bet the tflame was huge under the pot. But despite a big, hot flame, it wasn't having a lot of effect on the water inside because it didn't last long enough to do so. If that stove were to have about 1.5 ounces fuel in it, I bet you would reach boil in about 6 minutes.


When I put them at 1/2", both stoves boiled the water at 8 min and 20 sec, and burned for a total of 10 minutes. Remember, the only thing that changed was the pot height.


I assume the fuel amount was the same. Again, this is about what I have found. I also bet the flame came up the sides of the pot, but it wasn't as hot or as large as the flame previously was. Try reducing pot height to about 1/4" and you may be supprised - it should still boil, but take longer. The benifit again would be lighter weight and more stability, but at the expense of longer cooking times. What you may also find is you can boil with about 10ml - 12ml alcohol.


Anyway, I would appreciate anyone out there who would like to try this test using their favorite setup and then putting a spacer under the stove to set the pot height at 1/2", and report back the information here. Thanks again!


All that gets back to what I have been looking for in an efficient stove. To me it isn't about speed of boil, it is about weight and fuel efficiency. Add to that reliability and usefullness.

A Stove that CAN boil water in 5 minutes, may get under field conditions where it cannot, I have seen that. A stove too light and small may not work on under less than ideal conditions where it may tip - I've also seen that. I think so far the most relaiable and efficient stove I've made has been the Turbo V8, but I'm still playing with the Ion.



robbybob1

Thanks for sharing!

[SGT Rock]

By the way, this thread and the one on windscreens was the original reason I started a board wayyyy back. Thanks!

[robbybob1]

Thanks for the comments Sgt. Rock. I really appreciate all the work you have done in the area of Lightweight Stoves. You have really increased my knowledge and have sparked my interest in this area. I am going to continue to work on the "Flying Saucer" stove. Here is a photo of it as compared to a standard Pepsi Can Stove. Thanks again!

[SGT Rock]

Wow that is short. How do you keep the fuel in?

[robbybob1]

This stove will hold up to 1 fl oz of fuel, but it doesn't burn very efficiently. It takes a while to get primed, and when it does, liquid fuel comes out of the ports. At 1/2 fl. oz, it works just fine. My pot height test used that stove and it boiled at 8 minutes 20 secs with 1/2 fl. oz fuel. At 1/2 fl. oz, the fiberglass wick soaks up most of the fuel and leaves just enough to prime itself nicely.

[SGT Rock]

What is the bottom made from and how is it attached?

[robbybob1]

The bottom of the stove is made of the bottom of a soda can. The Top and Bottom are cut from Dr. Pepper cans at 9/16". The inner wall is about 3/4" tall. Construction technique is standard with JB Weld sealing the top and bottom outer walls. The inner wall is just fit into the groove tightly, with no JB Weld. Total weight is about 1/4 ounce.

[SGT Rock]

Wow, it looks too short for the bottom to be a soda can bottom. It looks totally flat.

[robbybob1]

Here is the top view photo.

[robbybob1]

And here is the Bottom View Photo.

[SGT Rock]

Got it. I made one like that just messing around, I never actually used it for anything. No JB weld anywhere, just pushed together and burned once.

BTW, aint it cool how you can show what you are talking about on this forum. Gotta love it.

[robbybob1]

The first one I made, I sealed the outer with Flue Tape. The thing leaked like a mutha. Good thing I had a cookie sheet under it. I decided to try the JB Weld seal on the outer and it worked like a champ. I haven't had any trouble with the Flue Tape on my standard size stoves, just the teeny one.